Disk drive read channel parasitics are a major limiting factor of further improvements in disk drive performance. The long wires that typically connect disk drive heads to interface electronics are a primary source of some of these parasitics. Also, typical yield loss for high sensitivity magnetoresistive vertical disk drive heads is over 33%. To better understand these problems, it is important to understand the following aspects of disk drive technology.
Disk drive memory systems (“disk drives”) have been a popular means for storing computer-generated information for many years. In magnetic disk drives, digital information is typically recorded as bits on concentric tracks on disks comprised of a material capable of maintaining a magnetic field. Each stored digital bit is represented by a region of magnetic particles on the disk. Whether the bit is a 1 or a 0 is indicated by the orientation of the magnetic field on the disk.
Common disk drives may include several disks mounted on a single spindle and stacked vertically, with a gap between each disk. Data is written to and read from the surface of each disk by means of a magnetic read/write head located on a load arm assembly. If two disks are use in a drive, a “E” assemble is used to provide a assembly for the disks. A mux circuit physically electronically located between the two disk is used to multiply the control signals and data signals for the heads. The mux current acts as leading factors in the place of any preamplifier circuit. In high performance, high-density hard disk drives, typically eight or more disks may be stacked on the same spindle. Since the read/write head must be able to fit between the disks to read or write data, the minimum distance possible between adjacent disks is limited by, among other things, the vertical thickness of the head-arm assembly. Data is typically stored on both sides of each disk. Therefore, there are usually two head-arm assemblies located in the gap between adjacent disks.
Prior art head-arm assemblies typically consist of a load arm, with a magnetic read/write head mounted on one end of the arm, and a miniflex interconnect, to connect the read/write head to the head interface electronics. The head interface electronics are typically mounted at the base of the head-arm assembly. Head interface electronics typically include a write current driver, a read amplifier, and a multiplexer for the write current driver, multiplexing and control circuitry. The write current driver provides the current required to produce a magnetic field to define the magnetic orientation of a region of particles on the magnetic disk. The read amplifier amplifies the small amplitude electrical signals produced by changes in the magnetic field orientation between regions of the magnetic recording disk. The multiplexing and control circuitry connect the write current driver and read amplifier to the selected read/write head or heads. Typically, the read/write head is connected to the interface circuit using thin wires. These thin wires often introduce parasitic capacitance and inductance into the read channel because of the relatively long length of the wires compared to the other read channel circuit components. These parasitic effects are undesirable because they may reduce the read channel's frequency response and available head voltage swing.
One conventional disk drive head is known as a vertical head. Magnetoresistive (MR) type vertical heads are currently in widespread use. MR vertical heads typically comprise a magnetoresistive read head and a traditional thin-film inductive write head. Vertical MR heads are typically manufactured using a semi-batch process in which head coils are deposited on a ceramic wafer (typically aluminum oxide or silicon carbide). These wafers are sliced into bars, which are turned 90 degrees for grinding. Photolithography and etching are then used to produce an air-bearing surface on one side of the bar. The bars are then diced into individual heads with read and write coils located at opposite ends of each head.
One way to improve data storage and retrieval speeds in a disk drive system, as well as the overall capacity of the disk drive, is to increase the rotational speed of the disks. Alternatively, the data density (digital bits/disk area) may be increased. However, the parasitics caused by the wires connecting the read/write head to the interface electronics limit the bandwidth and the minimum pulse amplitude that can be transmitted through the read channel. Thus, these wires limit the performance improvements that can be provided by increasing the disk speed or data density in a disk drive system.
High sensitive MR read heads have been developed to detect the low-level magnetic flux changes present on high-density data disks. These MR read heads improve disk drive performance by detecting the flux changes of smaller magnetic disk regions than could be accurately detected with the previous generation of MR read heads. Unfortunately, the magnetic sensitivity of these MR read heads also makes them highly sensitive to Electronic Static Discharge (ESD), the discharge of static electricity that results when a high voltage is formed from static electricity across a thin insulator region. When this ESD voltage exceeds a threshold voltage for that insulator region, the insulator breaks down, allowing a charge to move across the region to eliminate the voltage difference. This movement of the charge through the insulator generally destroys the sensitive circuit elements of the MR read head. ESD failures are a serious yield problem, and may cause MR read head yield losses as great as 60%. Thus, there is a need for a new disk drive head-arm assembly that both reduces the parasitics of the read channel and protects the head from ESD effects.
An alternative to a vertical head, called the planar head, has been developed for use in disk drive systems. One planar silicon head in use today is comprised of a nickel-iron coil deposited on the surface of a silicon wafer. Approximately twenty mask layers are required to construct the skis and air bearing surfaces on the wafer, and to deposit the read/write coils planar to the silicon surface. Unlike conventional vertical thin-film conductive heads, a single planar head typically performs both read and write operations.
Head-arm assemblies have been described with magneto-diodes or transistors deposited on the back side of the planar head wafer to provide preamplification and multiplexing functions to the heads while reducing the parasitics caused by connecting the head to a separate interface circuit. However, such techniques cannot be used with conventional vertical heads. Thus, an improved head-arm assembly is needed to reduce parasitics and improve the yield of conventional vertical heads.